1. Field of the Invention
This invention relates to fabrics having useful electrical properties.
2. Introduction to the Invention
Compositions which have a positive temperature coefficient of resistance ("PTC compositions") are known. They can be composed of ceramic material, eg. a doped barium titanate, or a conductive polymer material eg. a dispersion of carbon black or other particulate conductive filler in a crystalline polymer. The term PTC is generally used (and is so used in this specification) to denote a composition whose resistivity increases by a factor of at least 2.5 over a temperature range of 14.degree. C. or by a factor of at least 10 over a temperature range of 100.degree. C., and preferably both. The term switching temperature (or T.sub.s) is generally used (and is so used in this specification) to denote the temperature at which the sharp increase in resistivity takes place, as more precisely defined in U.S. Pat. No. 4,237,441. Materials, in particular conductive polymer compositions, which exhibit zero temperature coefficient (ZTC) behavior are also known. In electrical devices which contain a PTC element and a ZTC element, the term ZTC is generally used (and is so used in this specification) to denote an element which does not exhibit PTC behavior at temperature below the T.sub.s of the PTC element; thus the ZTC element can have a resistivity which increases relatively slowly, or which is substantially constant, or which decreases slowly, at temperatures below the T.sub.s of the PTC element. Materials, in particular conductive polymer compositions, which exhibit negative temperature coefficient (NTC) behavior are also known. For further details of conductive polymer compositions and devices comprising them, reference may be made for example to U.S. Pat. Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,861,029, 3,950,604, 4,017,715, 4,072,848, 4,085,286, 4,117,312, 4,177,376, 4,177,446, 4,188,276, 4,237,441, 4,238,812, 4,242,573, 4,246,468, 4,250,400, 4,255,698, 4,242,573, 4,271,350, 4,272,471, 4,276,466, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,361,799, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139, 4,459,473, 4,481,498, 4,476,450, 4,502,929, 4,514,620, 4,517,449, 4,545,926, 4,562,313, 4,571,481, 4,574,188, 4,582,983, and 4,659,913; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 now abandoned, published as German OLS No. 2,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz), now abandoned; 141,984 (Gotcher et al), published as European Application No. 38,718; 141,988 (Fouts et al) now abandoned, published as European application No. 38,718, 141,989 (Evans), published as European application No. 38,713, 150,909 (Sopory) now abandoned, published as UK application Nos. 2,076,106A, 184,647 (Lutz) now abandoned, 250,491 (Jacobs et al) published as European application No. 63,440, 272,854 and 403,203 (Stewart et al),published as European patent application No. 67,679, 274,010 (Walty et al), 300,709 and 423,589 (Van Konynenburg et al), published as European application No. 74,281, 369,309 (Midgley et al), 483,633 (Wasley), 509,897 and 598,048 (Masia et al) published as European application No. 84,304,502.2, 534,913 (McKinley) now abandoned, published as European application No. 84,306,456.9, 552,649 (Jensen et al) now abandoned, published as European application No. 84,307,984.9, 573,099 (Batliwalla et al) and 904,736, published as UK patent Nos. 1,470,502 and 1,470,503, and the three commonly assigned applications filed Sept. 14, 1984, Ser. Nos. 650,918, 650,920 and 650,919 (MP0959, 961 and 962). The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.